The present invention relates to a needle thread holding device in a sewing machine provided with a thread cutting unit. More particularly, the present invention relates to the needle thread holding device for holding a leading end portion of the needle thread which has been cut by the thread cutting unit in the sewing machine at a phase of completion of a sewing operation so that a minimized length of the cut end portion of the needle thread remains at a front side of a workpiece.
According to a conventional sewing machine having a thread cutting unit, a thread drawn from the lastly stitched point of a workpiece or a fabric is required to be cut when the sewing operation is terminated. For cutting the needle thread, Japanese Patent Application Kokai No. 56-139793 discloses a thread cutting mechanism in which upon completion of the sewing operation a movable blade is brought into engagement with a stationary blade by driving a rotating hook shaft for automatically cutting the needle thread and a bobbin thread at a position between a throat plate and a shuttle.
In a sewing machine provided with such thread cutting mechanism, if the needle thread length between a needle eye and the exact cutting point is insufficiently short, the needle thread may be easily disengaged from the eye of the needle at a start phase of subsequent or next sewing operation. That is, thread cast-off may occur. Therefore, the thread cutting must be made so that sufficient residual thread length can be provided between the needle eye and the exact cutting point in order to retain the thread to be still engaged with the needle eye at the start timing of the subsequent sewing operation.
However, if the residual thread length is excessively long, the residual needle thread may remain on a back surface of the workpiece, and the residual thread may be entangled with the bobbin thread at the subsequent sewing operation in a nest fashion as shown in FIG. 15, to thereby degrade stitching quality. In FIG. 15, the needle thread and the bobbin thread are represented by Ns and Bs, respectively, and the workpiece is designated by W.
To avoid these drawbacks, a thread holding device has been proposed in Japanese Patent Application Kokai No. 61-157487 which device avoids the needle thread cast-off from the needle eye at a first stitching, and also avoids entanglement of the needle thread and the bobbin thread at the back surface of the workpiece. In order to attain these objects, the disclosed device is provided with a thread holding unit and a thread trapping member. An end portion of the needle thread cut by a thread cutting mechanism at the terminal phase of the sewing operation is trapped by the thread trapping member at a position above the throat plate, and the trapped cut end portion of the needle thread is held by the thread holding unit in cooperation with the thread trapping member at a position largely spaced away from the sewing needle. The thread holding device is positioned remote from a needle location for the purpose of facilitating the workpiece handling or trimming, otherwise the thread holding device may become an obstacle for such workpiece handling.
In the conventional thread holding unit, a nest like thread entanglement is avoidable between the needle and bobbin thread at the back surface of the workpiece. However, in this device, since the needle thread length between the needle eye and the exactly cutting end portion is relatively long and the needle thread is held at a position greatly remote from the needle eye, relatively long needle thread may remain on the top surface of the workpiece as shown in FIG. 16. Therefore, thread pinching may be required. In FIG. 16, Ns, Bs and W designate the needle thread, the bobbin thread and the workpiece, respectively.
In order to avoid this drawback, Japanese Utility Model Application Kokai No. 62-109079 discloses a workpiece clamping unit provided with a needle thread holder, in which a thread cutting blade is provided at a pressure foot or a workpiece clamping member so as to cut the needle thread stitched and extending from the workpiece.
In this sewing machine, a special pressure foot must be provided so as to provide therein the thread cutting blade. Therefore, an ordinary or conventional pressure foot is not available in this sewing machine. Further, excessive tension may be applied to the needle thread at the time of the thread cutting, and therefore, a seam already provided on the workpiece may be disorganized or frayed. Moreover, the cut end portion of the needle thread may remain on the top surface of the workpiece as a waste thread.